Question: Joe started his math homework. He finished $23$ problems by himself. He finished $13$ more problems with help from Sal. There are $9$ math problems left. How many math problems did Joe have when he started?
Explanation: Joe completed ${23}$ problems by himself and ${13}$ problems with Sal. $?$ $23$ $13$ Problems done alone & with Sal solved by Joe solved with Sal ${23} + {13} = {36}$ Joe completed ${36}$ problems. Joe has $9$ problems left to solve. $?$ $36$ $9$ total problems problems solved problems left ${36} + 9 = 45}$ There were $45}$ total problems. Joe had $45}$ math problems when he started.